Here in the rainforests of Tambopata, we see many interesting relationships between different organisms. Some are just smaller than others.
If you think about it, nectar is typically pollinator bait- it draws insects like butterflies, beetles, and flies into the flower to drink, covering them in pollen, and helping the plant reproduce. However, pollination is not the only role that insects can play for plants- they can also be protectors.
What you are glimpsing above is an ant drinking out of an extra-floral nectary (EFN). An EFN is a fancy term for a source of nectar that lies outside the flower. These EFNs are typically located near the base of a leaf, or along an outer branch. Thus, any ant aiming to drink from it has to walk all the way up the entirety of the plant.
Camponotus femoratus ant feeding on an Inga extrafloral nectary.
The plant provides the sugar, the ant provides the protection.
Photo by Phil Torres
So why have an EFN? Over millions of years, a relationship can form between these ants and plants: the plants provide the nectar, and the ants provide protection. This nectar is even ant-diet specific, containing more sugar, and less amino acids, so they can have the energy to take down any herbivore that happens to attempt to feed on this plant.
The image shows an Inga sp. plant, however other plants can have relationships with ants that are even more complex than this. Some plants provide homes for them, some ants tend honeydew producing aphid 'cattle' on the plants, and some plants even reabsorb and 'eat' the anta' feces!
The ant in the image is only 3mm long. The well it is drinking out of, only about 1mm wide. Size clearly doesn't matter when it comes to interesting behavior.